1. Field of the Invention
The present invention relates to a high-efficiency fillet welding method for steel plate and, more particularly, to a high-efficiency fillet welding method for conducting arc welding of steel plates without requiring edge preparation.
2. Description of the Related Art
Architectural steel members are becoming thicker in accordance with the current tendency to build high rise buildings. For instance, steel plates used as the structural member of a so-called box post in such construction have thicknesses of about 100 mm, for example. Thicknesses of H-shapes are also increasing. As a consequence an unduly long time is required to build up and assemble such architectural steel members for high-rise buildings. This has given rise to a demand for improvement in the efficiency of the assembly procedure.
In general, fillet welding in fabricating a welded H-steel member, referred to as a "built-H" member, is conducted by partial penetration or full penetration welding. Full penetration welding is used when the web has a comparatively small thickness. For instance, Japanese Patent Publication No. 56-37029 discloses a method of preventing generation of pits and blowholes in welding primer coated steel plates which are 8 to 16 mm thick by employing small-diameter wires.
On the other hand, for welding thicker steel webs, the conventional method employs the steps of edge preparation, conducting welding on the obverse side, conducting gauging on the reverse side and effecting grinding and welding on the reverse side, thus attaining full penetration. Thus, the conventional method for making thick steel webs essentially requires expensive and time-consuming steps such as edge preparation, gauging and grinder finishing. For this reason it has been difficult to reduce the amount and cost of manual work and to improve arc time efficiency.
Attempts to attain partial or full penetration in fillet welding of steel plates, without conducting edge preparation and gauging, have encountered various problems which are still unsolved.
In general, melt-type fluxes are often used in fillet welding of thin H-shapes, because this type of flux has a low melting point and, hence, can suitably be used for high-speed welding. On the other hand, however, this type of flux tends to form narrow and convex beads as the welding speed is increased. In order to obviate this problem it has been proposed to cause the flux to foam to reduce the weight of the same thereby widening the weld beads. When this type of flux is used for welding thick steel members which require large welding heat input, the resulting amount of slag is unfavorably increased to an unacceptable level due to the low melting point of the flux, and as a result the appearance of the bead is impaired.
On the other hand, bonded fluxes, which are mix-bonded materials prepared from oxides, fluorides or carbonates, generally exhibit high melting temperatures and, therefore, are suitable for use for welding applications which require large heat input.
Welding without edge preparation also poses a problem in that the rate of dilution of the base metal is inevitably increased in order to attain the desired degree of penetration, so that hot cracking tends to occur particularly in steel plates having high carbon contents. Hot cracking tendency is closely related not only to the chemical composition of the weld metal but also to the cross-sectional shape of the bead. More specifically, hot cracking tends to occur when the penetration depth P is large for a given bead width W, i.e., when the ratio W/P between the bead width W and the penetration depth P is small. This means that the bead width should be increased as much as possible in order to prevent occurrence of hot cracking.